1. Field of the Invention
This invention relates to satellite control systems. More specifically, this invention relates to systems which protect satellite control systems from unauthorized use.
While the present invention will be described herein with reference to a particular embodiment in a particular application, it is to be understood that the invention is not limited thereto. Those having access to the teachings of the present invention will recognize additional embodiments and applications within the scope thereof.
2. Description of the Prior Art
The utility of satellites in providing a reliable, economical and secure link in small and large scale communication systems has been clearly demonstrated. As reliance on satellite communications has grown, so has the concern for maintaining control or command of the satellite. Obviously, maintaining reliable communications may be vital to national interest. This has raised concern about the extent to which a satellite may be equipped with safeguards against unauthorized intrusion or interference with its command system.
Conventional methods for protecting ground controlled satellites from unauthorized acquisition include the use of a coded command. A coded command is a complicated stream of data bits which when properly encoded identifies to the satellite that the following sequence of command signals is emanating from a friendly operator. In this context, if the proper bit sequence or code is not received, the satellite will ignore the subsequent commands. For such a system, the required electronic phase synchronization equipment is not only costly, but also adds weight to the system. Such equipment may, for example, reduce the payload by as much as 28 pounds.
While this technique may be desirable for a military satellite system, it tends to be too costly and unnecessarily complicated for a commercial satellite system. Thus, there is a need for a simple command protection system that does not add significantly to the cost or weight of the satellite communication system. Such a system is easily incorporated into a satellite which already has a beacon tracking system as that described in Applicant's copending application entitled "Two-Axis Antenna Direction Control System"; Ser. No. 246,793; filed Mar. 23, 1981 (now issued as U.S. Pat. No. 4,418,350).